To date, most AIDS prevention research has been conducted in large cities. However, there is also a need for prevention research focused in geographical areas were AIDS and HIV infection prevalence are still moderate, where risk behavior knowledge is limited, and where formal health resources concerning AIDS are also limited. Effective community behavior change programs practical in areas with low to moderate HIV infection prevalence may have substantial disease prevention impact. In the proposed study, a group of gay males in each of three medium-sized cities will be recruited to participate in a set of two training sessions. Participants will be individuals who are socially influential and who frequently interact socially with other gay males. The sessions will provide detailed educational training in AIDS transmission and high-risk activities, as well as social skills training to teach participants how to effectively communicate risk reduction information to others. Thus, participants will be made knowledgable about AIDS risk behaviors and will be specifically trained to educate peers, initiate discussions with gay and at-risk persons about risk reduction, and serve as a personally-known and credible source of accurate risk reduction information. Intervention will be implemented sequentially across the three cities in experimentally-controlled multiple baseline fashion. At points before and after intervention in each city, large-scale probe assessments will be made in social settings frequented by gay men in order to determine community knowledge about AIDS transmission and specific sexual activity behavior patterns related to AIDS exposure risk. If the intervention is effective, risk behavior and AIDS knowledge change should be detected for both training participants and for the large population of at-risk gay males in each city who are also assessed. Since training will be introduced sequentially across cities, it will be possible to establish that intervention is responsible for community behavior change. Because the intervention format is practical even for smaller cities, where prevention efforts are needed but prevention resources are often limited, the results of the study will be of direct relevance for public health agencies concerned about reducing AIDS spread. The intervention model to be tested is relevant for other AIDS at- risk groups such as IV drug users, where training "key" members of a population may be an effective way to reach the larger but more hidden proportion of the target population.